1. Field of Invention
This invention relates to an ad-hoc wireless network for a communication in a mobile environment. More specifically, the invention relates to establishment and maintenance of a moving-device to moving-device ad-hoc wireless network to achieve near-instantaneous communications.
2. Description of Related Art
Wireless technology has become common in all aspects of life today, whether it be a wireless home or office network, so-called “hotspot” networks at local cafes, fast food chains or hotels, or even citywide implementations of WiFi technologies. The aim of this wireless push in society is to provide accessibility to information and to increase the productivity that society as a whole has enjoyed through the wide acceptance and utilization of computer networks and especially the Internet. Wireless networking technology, such as 802.11a/b/g, allows WiFi-enabled devices to connect to each other as they would in a standard wired network without the restriction of wires. People are given the freedom to remain connected to a network regardless of their physical location within the network coverage area.
With this goal in mind, several cities have attempted to create a wireless network for the city. For example, on Jul. 29, 2004, Grand Haven, Mich. claimed the distinction of being the “first WiFi city in America” with its implementation of a citywide wireless network covering the 6 square miles of the city and extending 15 miles into Lake Michigan. Many city officials see WiFi as an infrastructure necessity, much like sewage, power, telephone and transportation, for attracting and retaining business. The benefits of such systems for the city administrators are many, ranging from providing communication among city employees to providing public service announcements, advisories and other useful information to the citizenry at large.
In this drive for greater wireless connectivity, one area of everyday life has lagged behind. The roads and highways of America have remained largely untouched by wireless technology beyond rudimentary satellite and cellular phone systems. However, there are many advantages to be gained from wireless network technology implementations on American roads. Among the most notable are traffic advisories, Amber alerts, weather advisories, etc., which could be relayed to all vehicles that may be affected on an immediate basis.
Further, networking automobiles together allows the relay of information about a vehicle that may affect other vehicles in the vicinity. For example, an automobile may suddenly brake; this action could be reported to all vehicles behind the braking automobile instantaneously, thus allowing the drivers of the other vehicles to take necessary action with less urgency. This aspect has clear implications for reducing traffic accidents and congestion. This type of wireless networking may appear in many aspects of vehicle safety applications, including, but not limited to, urgent road obstacle warning, intersection coordination, hidden driveway warning, lane-change or merging assistance.
Vehicle safety communications (“VSC”) may be broadly categorized into vehicle-to-vehicle and vehicle-with-infrastructure communications. In vehicle-to-vehicle communication, vehicles communicate with each other without support from a stationary infrastructure. Vehicles communicate with each other when they are within the same radio range of each other or when multiple-hop relay via other vehicles is possible. In vehicle-with-infrastructure communication, vehicles communicate with each other with the support of infrastructure such as roadside wireless access points. In this case, vehicles may also communicate with the infrastructure only.
Key VSC performance requirements include low latency (on the order of 100 mili-second) and sustained throughput (or equivalently, the percentage of neighboring vehicles that successfully receive warning messages) in order to support various VSC applications such as collision avoidance.
Simply installing wireless antenna on a moving vehicle and then transmitting uncoordinated communications would not suffice for satisfying these requirements. Specifically, by transmitting uncoordinated data, the airwaves would be flooded with a plurality of messages, which would result in a jamming of the radio waves, as the radio bandwidth is limited.
As such, these vehicles would interfere with each other's transmission and compete with each other for radio bandwidth for transmission. Further, all messages would propagate in all directions without any consideration of a desired transmission direction.
Additionally, each vehicle would not match other vehicles' network configurations.
The high mobility and lack of inherent relationships make a priori configuration of vehicles into vehicle groups problematic (e.g., no vehicle knows anything about its neighbors beforehand). All information that is necessary for setting up safety communications must be exchanged in near real-time among vehicles, and vehicles in the groups must configure themselves in near real-time so that safety communication can take place. The high mobility of uncoordinated vehicles implies frequent change of neighbors or vehicle groups, and poses difficulties of using support-servers (for mobility, address, name, media session) within vehicle groups. These key differences make existing tactical ad-hoc networking technologies not directly applicable to vehicle groups for safety communications.
Using WiFi methods employed elsewhere, such as hotspots, are impractical because of coverage, data traffic volume and latency issues. A normal rush hour commute around a major city could yield a vehicle density of as much as 600 vehicles per 1200-meter length of a 3-lane highway. In addition, all these vehicles are moving through individual coverage areas at a rate of 30 to 60 mph. Most wireless systems are not equipped to handle such a large rate of change in their network.
Specifically, as a vehicle enters the coverage area, it would need to be identified and issued configuration instructions by a wireless access point or router. When a vehicle leaves the coverage area, the wireless access point or router would need to update its records to remove the vehicle form its network. Thus, the speed of a vehicle through a particular coverage area determines how often updating information, e.g. handshaking, needs to be broadcasted by the wireless access point or router and responded to by all the vehicles in range. All these vehicles transmitting information at the same time could very easily overwhelm the system in short order.
Several attempts have been made to establish a vehicle-to-vehicle communication network. For example, FleetNet and CarTalk2000 have both developed a vehicle-to-vehicle communication network. Both of these systems used a GPS system in each vehicle for location information. FleetNet uses both fixed and moving nodes as the infrastructure for “ad-hoc” networks. The fixed node can act as a server router, a gateway router and a client server router. This use of a plurality of fixed nodes causes a significant financial cost and overhead to set up, maintain, and manage the infrastructure. Additionally, the FleetNet system uses position based routing and location awareness. Specifically, as the backbone for their system, position data plays a crucial role in the communication protocols deployed.
CarTalk 2000 also uses a position-based protocol. Each vehicle participating in the CarTalk2000-based inter-vehicle system must be equipped with GPS devices to detect its current position at any given time. Additionally, CarTalk2000 uses multiple different routing protocols, such as topological information routing, procedure routing, and reactive routing—such as Ad-hoc On-demand Distance-Vector Protocol, Dynamic Source Routing, hybrid routing, etc. Each of these routing protocols uses a complex and distinct set of protocol rules.
A major drawback of the CarTalk2000 system is the discovery of neighboring nodes significantly increases bandwidth traffic. Each node periodically sends a beacon to its neighboring cars reporting its existence. In high traffic areas this would result in constant beacon message collision.
However, these GPS networks have a significant drawback. In a high-mobility vehicle environment, the GPS information quickly becomes outdated. The exchange of constantly changing GPS information among vehicles, in order to perform GPS-positional routing, incurs too much protocol overhead and wireless bandwidth waste. As a result, such GPS-positional routing technology cannot achieve minimal communication latency or sustained multiple-hop throughput.
Accordingly, there exists a need to create an ad-hoc network capable of achieving the stringent VSC performance requirements while achieving minimal communication latency or sustained multiple-hop throughput without requiring excessive bandwidth and significant protocol overhead.